BRPI0308336B1 - process for catalytic oxidation in vapor phase - Google Patents

Abstract

"process for catalytic oxidation in vapor phase". The present invention provides a process for catalytic vapor phase oxidation which prevents the disordered reaction or early deterioration of a catalyst in the production of (meth) acrylic acid or the like from propylene or isobutylene by a catalytic oxidation process. in vapor phase using a multitubular reactor, which can provide constant production in high yield for a long period of time. furthermore, the present invention provides a process for catalytic vapor phase oxidation in which the gaseous feedstock is introduced for oxidation into the reaction tubes of a multitubular reactor which is equipped with several tubes disposed within the reactor shell. having a catalyst filler on them and several baffle plates to change the flow direction of a heating medium introduced into the shell, characterized in that the temperature of the catalyst filler in a reaction tube, which is not connected with at least one deflector plate, is measured at plural points in the direction of one axis of the reaction tube.

Description

Patent Descriptive Report for "VAPOR CATALYTIC OXIDATION PROCESS".

TECHNICAL FIELD The present invention relates to a process for catalytic vapor phase oxidation which prevents uncontrolled reaction or early deterioration of a catalyst in the production of (meth) acrylic acid or the like from propylene or isobutylene by of the process for catalytic vapor phase oxidation using a multitubular reactor, which makes production constantly in high yield for a possible long period of time.

BACKGROUND OF THE INVENTION

A usual multitubular reactor has a structure which is equipped with, disposed within the reactor shell, a plurality of reaction tubes having a catalyst filler therein and a plurality of baffle plates having openings to distribute an introduced heating medium. in the hull, entirely in the hull. It was common that the temperature of the heating medium flowing into the hull was measured and, based on the measurement result, the operational control of the multitubular reactor was conducted, while the temperature of the heating medium in the hull was uniformly controlled. Most of the reaction tubes arranged in the shell are connected to the baffle plates. However, some of the reaction tubes passing through the openings formed in the baffle plates are not connected to them. The catalyst layers in the reaction tubes, which are not in contact with the baffle plates, tend to have localized heat accumulation points (hot spots) formed due to the reaction heat. If a hot spot formed, the catalyst portion tended to deteriorate due to excessive thermal generation and the service life tended to decrease.

In addition, in order to achieve adequate catalyst life performance by preventing hot spot formation, it was necessary to decrease the concentration of gaseous raw material translated into the reaction tubes, or to limit the amount introduced, whereby there could be a case in which (meth) acrylic acid or the like could not be constantly produced in high yield over a long period of time.

DESCRIPTION OF THE INVENTION The present invention provides a process for catalytic vapor phase oxidation using a multitubular reactor whereby the problems mentioned above can be solved, the summary of which is given below. (1) A process for catalytic vapor phase oxidation, in which the gaseous feedstock is introduced for oxidation into the reaction tubes of a multitubular reactor, which is equipped with several filled reaction tubes disposed within the reactor shell. of catalyst in them and various baffle plates to vary the flow direction of a heating medium introduced into the shell, characterized in that the temperature of the catalyst filler in a reaction tube, which is not connected with at least one baffle plate, It is measured. (2) A process for catalytic vapor phase oxidation, in which the gaseous feedstock is introduced for oxidation into the reaction tubes of a multitubular reactor, which is equipped with several reaction tubes filled within the reactor shell. of catalyst in them and various baffle plates to vary the flow direction of a heating medium introduced into the shell, characterized in that the temperature of the catalyst filler in a reaction tube, which is not connected to at least one baffle plate , and the temperature of the catalyst filling in a reaction tube, which is connected with all baffle plates, is measured. (3) The process according to item (1) or (2), wherein the temperature or flow rate of the heating medium to be introduced into the shell is controlled based on the measured temperature of the catalyst. (4) The process according to any of (1) to (3), wherein the catalyst temperature is measured at 2 to 20 points in the direction of the reaction tube axis. (5) The process according to any one of (1) to (4), wherein the catalyst temperature is measured using a multipoint thermocouple. (6) The process according to any of (1) to (5), wherein the direction of the flow of gaseous raw material flowing into the reaction tubes and the direction of a macroscopic flow of the medium. warming, which seeps into the hull, are identical. (7) The process according to any one of (1) to (6), wherein several layers of catalyst, which have different activities, are filled in the reaction tubes. (8) The process according to any one of (1) to (7), wherein the gaseous feedstock contains propylene, isobutylene or (meth) acrolein as a material to be oxidized.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1: Cross-sectional view of an example of a multitubular reactor to be used for a process for catalytic vapor phase oxidation.

Figure 2: Perspective view of an example of deflector plates equipped with a multitubular reactor.

Figure 3: Perspective view of another example of baffle plates equipped with a multitubular reactor.

Figure 4: View of the multitubular reactor of Figure 1 seen from above.

Figure 5: Cross-sectional view of another example of a multitubular reactor to be used for a process for catalytic vapor phase oxidation.

Figure 6: Partial sectional view of an intermediate tubular plate and thermal protection plates fitted to a multitubular reactor of Figure 5.

Explanation of reference symbols 1a, 1b, 1c: reaction tube. 2: multitubular reactor shell. 5a, 5b: tubular plate. 6a, 6b: baffle plate. 9: intermediate tubular plate. 11: thermometer for catalyst. 14.15: thermometer for heating medium.

Hm: heating medium.

Rg: gaseous raw material.

METHOD FOR CARRYING OUT THE INVENTION The process for catalytic vapor phase oxidation of the present invention will be described based on the accompanying drawings. The process for vapor catalytic oxidation of the present invention and a multitubular reactor to be used for the catalytic vapor phase oxidation process will be described based on Figure 1. Number 2 designates a hull for the multitubular reactor at which reaction tubes 1a, 1b and 1c, which have a catalyst filler therein, are attached to both the lower tubular plate 5b and the upper tubular plate 5a.

At the top and bottom ends of the hull 2, inlet and outlet ports 4a and 4b for the gaseous feedstock Rg for the reaction are provided, and the gaseous feedstock Rg flows into the reaction tubes 1a, 1b and 1c in the up or down flow direction. This flow direction is not particularly limited, but upward flow is particularly preferred.

In addition, a circular conduit 3a for introducing the heating means Hm is provided on the outer periphery of the hull 2, and the heating means Hm having increased pressure by the circulation pump 7 is introduced into the hull 2 of the circular conduit. 3rd The heating medium introduced into the hull 2 flows upwards, while the flow direction is changed by the baffle plates 6a, 6b and 6a as indicated by the arrow indications. Meanwhile, the heating medium Hm absorbs reaction heat through contact with the outer surfaces of the reaction tubes 1a, 1b and 1c, and is then returned to the circulation pump 7 via the circular conduit 3a provided at the periphery. external hull 2.

A portion of the reaction heat absorbing heat medium Hm is fed to an exhaust duct 8b provided at the top of the circulation pump 7 to be cooled by a heat exchanger (not shown) and then to the circulation pump 7 by supplying a heating medium supply conduit 8a to be reinserted into the hull 2. The temperature control for the heating medium Hm introduced into the hull 2 is conducted by controlling the temperature or flow volume of the heating medium to be drained from the heating medium supply conduit 8a. In addition, the temperature of the heating medium Hm is measured by a thermometer 14 inserted in the inlet side of the circular conduit 3a.

In each copper plate within the circular conduits 3a and 3b, a rectifying plate (not shown) is provided to minimize circumferential distribution of the heating medium flow. As such, a grinding plate, for example a porous plate or a plate having grooves is employed. By varying the opening area of the porous plate or the distance of the grooves, the heating medium Hm is rectified so that the heating medium can be introduced into the shell 2 of its entire periphery with constant flow and volumetric flow. constant. In addition, several thermometers 15 are arranged at regular intervals in a circumferential direction, as shown in Figure 4, whereby the temperature in the circular duct (3a, particularly 3b in addition to it) can be monitored.

In general, at least three baffle plates (6a, 6b and 6a) are usually arranged in hull 2. Due to the presence of the baffle plates, the flow of heating medium Hm in the hull 2 is such that it is first routed from the peripheral portion to the shell. central portion of the hull 2, and then is directed to the outer periphery as it flows upwardly through the opening portion of the baffle plate 6a to reach the inner wall of the hull 2.

Then, the flow direction of the heating medium Hm is changed again, while the medium flows through the space between the inner wall of the hull 2 and the outer periphery of the baffle plate 6b, and then is routed to the central portion. It then flows through the opening portion of the baffle plate 6a, flows along the lower surface of the upper tubular plate 5a into the shell 2 to be directed to the outer periphery, is introduced into the circular conduit 3b, and finally is sucked into the pump. circulation 7, to be circulated again in the hull 2.

As the specific deflector plate structures to be used in the present invention, segmented beveled circular deflector plates as shown in Figure 2 or circular deflector plates as shown in Figure 3 can be applied. relationship between the flow direction of the heating medium and the reaction tube axis.

The baffle plates 6a have their outer peripheries coincident with the inner wall of the hull 2 and have an opening portion near the center. In addition, the diameter of the outer periphery of the baffle plate 6b is smaller than that of the inner wall of the hull 2, whereby a gap is formed between the outer periphery of the baffle plate 6b and the inner wall of the hull 2. Heating medium is altered by varying flow direction, while heating medium flows through respective opening and space portions.

A thermometer 11 is inserted into each of the reaction tubes 1a, 1b and 1c disposed in the shell 2, and signals are transmitted to an outer portion of the shell 2, whereby each temperature distribution in the direction of the tube axes in the layers. of catalyst fillings in reaction tubes is measured.

Multipoint type thermometers or movable thermometers 11 on a jacket to measure a plurality of points are inserted into reaction tubes 1a, 1b and 1c whereby temperatures at 2 to 20 points in the direction of the axes are measured. The internal space of the hull 2, equipped with reaction tubes 1a, 1b and 1c, is divided by three baffle plates 6a, 6b and 6c, and the divided spaces are classified into 3 types with respect to the direction of flow of the heating medium. Hm.

That is, the reaction tube 1a is connected to the baffle plate 6b, whereby the flow direction of the heating medium Hm is limited only by the baffle plate 6b, and the flow direction is not limited by the other two baffle plates 6a, once it passes through the opening portions of these baffle plates 6a. The heating medium Hm, introduced from the circular conduit 3a into the hull 2, varies its flow direction in the central portion of the hull 2, as indicated by the arrow indications in Figure 1. In addition, the reaction tube 1a is positioned that the flow direction is changed, whereby the heating medium Hm, which flows around the outer periphery of the reaction tube 1a, basically flows parallel to the axis of the reaction tube 1a. The reaction tube 1b is connected with three baffle plates 6a, 6b and 6a, whereby the flow direction of the heating medium Hm is limited by the respective baffle plates. In addition, the flow of heating medium Hm, which flows around the outer periphery of reaction tube 1b, flows perpendicular to the axis of reaction tube 1b at approximately all positions of reaction tube 1b. Here, most of the reaction tubes arranged in the hull 2 are in positions corresponding to the reaction tube 1b.

In addition, the reaction tube 1c passes through the space between the outer periphery of the reaction tube 6b and the inner wall of the shell 2, without any contact with the baffle plate 6b, whereby the flow of the heating medium Hm, in position , is not limited by the baffle plate 6b, and flows parallel to the axis of the reaction tube 1 c. Figure 4 shows the interrelationship between the positional relationship of reaction tubes 1a, 1b and 1c and baffle plates 6a, 6b and 6a and heating medium flows Hm.

When the opening portion of the baffle plates 6a (the innermost circle of the dotted line) is the direction position of the heating medium Hm, that is, in the center of the shell 2, the heating medium Hm does not flow merely parallel to the heating tube. reaction 1a, but also flows with difficulty into the center of the opening portion of the baffle plates 6a, that is, the flow rate is approximately zero, whereby the thermal conductivity efficiency is terribly poor. Therefore, there is a case in which the reaction tube 1a is not disposed in this position. Figure 5 is another example of the present invention, in a case in which the inner portion of the reactor shell 2 is divided by an intermediate tubular plate 9.

In the divided spaces of the hull 2, the heating means Hrrii and Hrri2 are circulated respectively and, furthermore, subjected to temperature controls respectively.

The upper and lower portions of the reaction tubes 1a, 1b and 1c are divided by interposed layers of an inert material, which are not involved in the reactions, different catalysts are stuffed in them respectively, and the temperatures of the respective catalysts are controlled under different conditions. optimal conditions to drive the reactions. In addition, the position for interposition of this inert material is a portion corresponding to the positions at which the outer peripheries of reaction tubes 1a, 1b and 1c are in contact with intermediate tubular plate 9. Gaseous feedstock Rg is introduced from a gaseous feedstock input 4a, and then reactions are conducted sequentially as gas flows into reaction tubes 1a, 1b and 1c to produce a product.

For example, propylene or isobutylene is introduced as a gas mixture with molecular oxygen containing gas, then converted to (meth) acrolein at the bottom, and then oxidized at the top to form (meth) acrylic acid.

In Figure 6, number 9 designates an intermediate tubular plate, three thermal protectors 10 are secured at positions below the lower surface of the intermediate tubular plate 9 by means of spacer rods 13. Two or three thermal protectors 10 are provided below the tubular plate. intermediate 9, as shown in this figure, or above it at positions equally no more than 100 mm, whereby stagnation spaces 12 are formed, having no flow, even though the heating medium Hmi or Hm2 is placed. Accordingly, it is preferred to leave the spaces having a thermal insulation effect.

The reasons why the thermal protectors 10 are attached to the intermediate tubular plate 9 are as follows. That is, in Figure 5, in a case where the difference in controlled temperatures between the heating medium Hmi introduced at the bottom of the hull 2 and the heating medium Hm2 inserted at the top exceeds 100 ° C, Thermal transfer from a hot to low temperature medium is not disregarded, whereby the accuracy of catalyst reaction temperature control on a low temperature side is impaired. In this case, thermal insulation must be provided to prevent thermal transfer above and / or below the intermediate tubular plate 9.

In the multitubular reactor to be used for catalytic vapor phase oxidation, a mixed gas is introduced as the gaseous reaction raw material Rg, wherein the mixed gas comprises propylene or isobutylene, and / or (meth) acrolein mixed with gas or vapor containing molecular oxygen. The concentration of propylene or isobutylene is 3 to 10% by volume, and oxygen is 1.5 to 2.5 (molar ratio) and steam is 0.8 to 2 (molar ratio), both for propylene. or isobutylene. The gaseous feedstock Rg introduced therein is divided by the respective reaction tubes 1a, 1b and 1c, and then, as it flows into the reaction tubes, reacted by an oxidation catalyst contained therein. However, the distribution of the gaseous feedstock Rg to the respective reaction tubes is affected by, for example, filling quantities or catalyst filling densities in the reaction tubes. These amounts of catalyst filling or filling densities are determined when the catalyst filling operation in the reaction tubes. Therefore, it is very important to fill the catalyst evenly in the respective reaction tubes.

In order to uniformly fill the catalyst, it is possible to employ a process of producing a constant filling density, for uniformizing the weight of the filled catalyst in the respective reaction tubes, or for adjusting the catalyst filling time to be the same. The gaseous feedstock Rg, which flows into the respective reaction tubes 1a, 1b and 1c, is first heated during flow by the stuffed inert agent layer at each inlet part to reach the reaction starting temperature. The raw material (propylene or isobutylene) is oxidized by the catalyst contained as the next layer in each reaction tube, and the temperature is further increased by the heat of the reaction. The amount of reaction is greater at the inlet portion of the catalyst layer, and if it exceeds the amount of heat removal by the heating medium Hm, the generated reaction heat will serve to increase the temperature, with which a point may be formed. hot. The hot spot will also be formed at a position of 300 to 1,000 mm from the reaction tube inlets 1 a, 1 b and 1 c.

Consequently, the thermal removal effect by the flow of the heating medium Hm is most important within 1,000 mm of the reaction tube inlets 1a, 1b and 1c. If the amount of reaction heat generated in them exceeds the thermal removal capacity of the heating medium Hm from the periphery of the reaction tubes, the temperature of the gaseous raw material will increase further, whereby the amount of reaction heat generated will increase. increase further, and finally, an uncontrolled reaction will occur. Thus, it is possible for the catalyst temperature to exceed the maximum allowable temperature, and the catalyst undergoes a quality change, with deterioration or rupture of the catalyst.

With respect to the preliminary step reactor for acrolein production by the propylene oxidation reaction with the molecular oxygen containing gas, as an example, the temperature of the heating medium Hm is from 250 to 350 ° C, and the maximum allowable temperature near the hot spot is 400 to 500 ° C.

In addition, with respect to the reactor of the subsequent step, to obtain acrylic acid by acrolein oxidation with the gas containing molecular oxygen, the temperature of the heating medium Hm is from 200 to 300 ° C, and the maximum allowable temperature near the point. hot is from 300 to 400 ° C.

As heating medium Hm, which flows into hull 2, ie around the outer peripheries of reaction tubes 1a, 1b and 1c, Niter, which is a mixture of nitrates, is widely used, but a heating medium of Phenyl ether from an organic liquid system can also be used. Heat removal is conducted on the outer peripheries of reaction tubes 1a, 1b and 1c during the flow of heating medium Hm. However, with respect to the heating medium Hm introduced from the circular conduit 3a to the hull 2, a position in which the medium flows from the outer periphery of the hull 2 to the central part, and a position in which the direction of flow is rotated in direction. around the central portion are present, and it has been found that the effect of thermal removal is extremely different in their respective positions.

When the flow direction of the heating medium Hm is perpendicular to the axis of the reaction tube, the heat transfer coefficient is 1,000 to 2,000 W / m2 ° C. However, when the direction of flow is not perpendicular to it, it differs according to the flow or difference of upstream or downstream. However, even though Niter is used as a heating medium, the heat transfer coefficient is usually at most 100 to 300 W / m2 ° C.

On the other hand, the heat transfer coefficient of the catalyst layers in reaction tubes 1a, 1b and 1c is naturally based on the flow rate of the gaseous feedstock Rg. However, it is approximately 100 W / m2 ° C, which obviously does not depart from a conventional knowledge that what controls the heat transfer rate is the gas phase in the pipes.

Specifically, when the flow of the heating medium Hm is perpendicular to the axes of the reaction tubes 1a, 1b and 1c, the heat transfer resistance of the outer periphery of the tube is 1/10 to 1/20 of that on the gas side Rg of the reaction tube. Although the flow rate of the heating medium Hm will change, this variation will not substantially affect the resistance to global heat transfer.

However, when Niter flows parallel to the tube axes, the heat transfer coefficients inside and outside the reaction tubes 1,1b and 1c are approximately equal, whereby the influence of the flow state at the outer periphery of the tubes on the efficiency of the Heat removal is substantial. That is, when the heat transfer resistance of the outer periphery of the pipe is 100 W / m2 ° C, the overall heat transfer coefficient is half of it, and even more, half of the change in heat transfer resistance of the outer periphery of the pipe is 100 W / m2 ° C. tube influences the overall heat transfer coefficient. It is necessary to monitor the difference in heat transfer coefficients carefully when the reaction is conducted in practice. Reaction tube 1b is one bounded by all deflector plates (usually three sheets), in which the overall heat transfer coefficient is large, the maximum temperature is low in the temperature distribution in the direction of the axis of the tube. catalyst layer in the reaction tube, and is considered to be an average across the hull 2.

In addition, the reaction tube, which is provided in a position in which the heating medium Hm changes direction, is reaction tube 1c not bound by a baffle plate, or reaction tube 1a not bound by two baffle plates. .

When the amount of gaseous feedstock Rg supplied to reaction tubes 1a, 1b and 1c is increased, or the reaction temperature is kept high for high conversion, the maximum reaction tube temperature tends to increase. , to form hot spots, whereby the possibility of catalyst deterioration or uncontrolled reaction will increase.

In this case, the temperature of the heating medium Hm must be strictly controlled. A plurality of thermometers 11 are inserted into a plurality of reaction tubes 1a or 1c, and the temperature of the heating medium Hm is controlled as simultaneous monitoring of the hot spot temperatures of the respective reaction tubes. The temperature of the heating medium Hm is thus strictly controlled to a more suitable temperature, whereby a resulting desired reaction can be obtained, and furthermore, for example, it is possible to prevent catalyst deterioration, and to be possible. conducting continuous operation for a long period of time.

When the maximum temperature of reaction tube 1a is close to the temperature limit, the temperature of the heating medium Hm may be lowered. However, in the case of reaction tube 1c, there may be a case in which the temperature of the downstream portion of the position having the maximum temperature will increase. Therefore, contempt of monitoring is not possible.

When the conversion by reaction is lower than the most suitable value, the temperature of the heating medium Hm must be increased. However, even at this time, it is important to monitor the maximum reaction tube temperature so that it does not exceed the limit temperature. Further, the maximum temperature of the reaction tube, or position showing the maximum temperature of the reaction tube, may sometimes vary, also when the amount supplied to the hull 2 of the gaseous feedstock, such as a propylene or isobutylene mixed gas oxygen-containing gas or the like increases or decreases.

In addition, it is particularly preferred that thermometers 11 are also inserted into a plurality of reaction tubes 1b, and the temperature of the heating medium Hm is controlled while monitoring the temperatures of the catalyst layers in the reaction tubes. The maximum temperature of reaction tubes 1b, which occupy the vast majority of reaction tubes, is measured and compared to the maximum temperature of reaction tubes 1a or 1c in other areas, which gives the most appropriate reaction result. . The difference in the maximum average temperature (the average maximum temperature for each reaction tube) of the reaction tubes present in the respective areas is preferably within 30 ° C, particularly within 20 ° C and especially within at 15 ° C. If the difference is too large, the reaction yield tends to decrease, which is undesirable. The number of reaction tubes 1a, 1b and 1c having thermometers 11 inserted in their respective areas is at least 1 and preferably from 3 to 5. If the number entered is some, there may be a case in which the abnormality the maximum temperature of the reaction tubes is not detected, even if there is a temperature unevenness of the heating medium Hm introduced in the circular conduit 3a of the shell 2.

In addition, the above area is intended for aggregation of reaction tubes, which extend through an opening or space of the same baffle plate, and are further connected and supported by the same baffle plate.

The types of baffle plates for the purpose of changing the flow direction of heating medium Hm, flowing into the shell 2, or preventing a flow of heating medium bypass Hm are not particularly limited. However, a segmented baffle plate or a circular baffle plate as shown in Figure 2 or 3 is employed, and particularly the circular baffle plate appears to be widely used. The opening area in the center of the baffle plate 6a is from 5 to 50%, preferably from 10 to 30% of the hull 2 inner cross-sectional area. The spatial area formed by the outer periphery of the baffle plate 6b and the inner wall hull 2 is from 5 to 50%, preferably from 10 to 30% of the hull 2 inner cross-sectional area.

If the ratio of the openings and the spatial relationship of the baffle plates 6a and 6b are too small, the flow path of the heating medium Hm will be long, the pressure loss between the baffle plates 3a and 3b will increase and the power of circulation pump 7 will increase. On the other hand, if the ratios are too large, the number of reaction tubes 1a and 1c will increase. The spacing of the respective baffle plates (the distance between the baffle plates 6a and 6b, the distance between the baffle plate 6a and the upper tubular plate 5a and the distance between the baffle plate 6a and the lower tubular plate circulation pump 7) is usually set to be at equal intervals. However, it may not necessarily be adjusted to be an equal range as long as the required flow rate of the heating medium Hm, determined by the heat of the oxidation reaction generated in the reaction tube, can be maintained, and the pressure loss of the medium. heating can be decreased. The maximum temperature position in the temperature distribution in the reaction tubes 1a, 1 b or 1c must not be the same as the position of the baffle plate 6a, 6b or 6a. Near the surface of each baffle plate, the flow rate of the heating medium decreases and the heat transfer coefficient will be low. Consequently, if the maximum temperature position of the reaction tube has been superimposed on it, a hot spot is highly likely to form.

In hull 2, within the reaction tubes 1a, 1b and 1c, containing the oxidation catalyst, is a gas phase and, furthermore, the maximum linear velocity of the gas raw material is limited by the catalyst, whereby the coefficient of Heat transfer in the respective reaction tubes will be low, and turns into a heat transfer control process. Consequently, the inside diameters of the reaction tubes are very important.

The inside diameters of reaction tubes 1a, 1b and 1c are affected by the amount of reaction heat and catalyst particle diameter in the tubes. However, an internal diameter of 10 to 50 mm is usually selected. It is particularly 20 to 30 mm. If the internal diameters of the respective reaction tubes are too small, the weight of the catalyst filler in them will decrease and the number of reaction tubes will be large for the required catalytic amount, with the hull 2 will be large.

On the other hand, if the inside diameters of the reaction tubes are too large, the contact of the catalyst and surface area of the reaction tube will be small for the amount of heat removal required, so the heat transfer efficiency for removal. Heat of reaction heat will decrease.

As the thermometer 11 is inserted into the reaction tube, usually one having a columnar shape, in which several thermocouples, thermal resistance sensors or the like are covered with an outer tube (thermal well), or one in which a thermocouple is movable in the jacket. can be used. Thermometer 11 must be placed in a position on the tube axis and projections are provided on the surface of the reaction tube, whereby the distance from the inner wall of the reaction tube is limited to overlap the position of the tube axis. .

It is preferred that the reaction tube tube axis and the thermometer center axis 11 are overlapping. In addition, it is preferred that the projections, which are formed on the thermometer 11, be provided at the front and rear of the maximum temperature position in the catalyst layer.

Like the outer tube (thermal well) of thermometer 11, one having a maximum diameter of 15 mm is used. Also, considering the relationship to the inside diameter of the reaction tube, the distance to the inside wall of the reaction tubes should be at least twice the catalyst particle diameter. If the catalyst particle diameter is 5 mm and the inner diameter of the reaction tube is 30 mm, the outer tube diameter of thermometer 11 must be a maximum of 10 mm.

If the density of the catalyst filling is different between the reaction tube having a thermometer 11 inserted and the other reaction tube, the precise temperature cannot be measured. Accordingly, the outside diameter of thermometer 11 is preferably at most 6 mm, particularly 2 to 4 mm. The present invention is basically to take measures to satisfy the situation by analyzing the flow rate and heat transfer coefficient of the heating medium Hm, and to evidence the presence of a portion having a low heat transfer coefficient in the respective portions in However, with respect to the reaction tube disposed in the portion having a low heat transfer coefficient, particularly with respect to reaction tube 1a and a reaction tube in its vicinity, an area having a coefficient extremely low heat transfer is found in the opening portion of the deflector plate (the round center portion in the circular deflector plate), in the center or in its vicinity, in the cross section of the hull 2. This area is found at or near the center of the deflector plate. opening portion of the baffle plate 6a. Therefore, it is recommended that no reaction tube be provided in this area, corresponding to a portion having a hull cross-sectional area ratio of 0.5 to 5%. If this portion is less than 0.5%, the amount of flow of the heating medium Hm must be adjusted to be at least twice so that the heat transfer coefficient is at least the minimum required, whereby the power of the circulation pump 7 will have to be increased.

However, if the area in which no reaction tube was provided is greater than 5%, the hull 2 waist diameter will need to be increased to provide the required number of reaction tubes.

With respect to reaction tubes 1a, which are not supported by the baffle plate 6a, it is preferred not to provide them at 30 to 80% of the opening portion width of the baffle plate 6a (in the case of the segmented baffle plate of Figure 2) or of the opening portion diameter of the baffle plate 6a (in the case of the circular baffle plate of Figure 3).

In Figures 1 to 5, the upward flow direction of the gaseous raw material in hull 2 is shown by the arrow indications. However, the present invention may also be applied to a case in which the direction of flow is opposite.

When the direction of flow of the heating medium Hm is to be determined, care must be taken to avoid a phenomenon where gas, which may be in the upper portions of the hull 2 and the circulation pump 7, particularly the Inert gas, such as nitrogen, will be included in the flow of the heating medium.

In a case where the heating medium Hm is upstream, as shown in Figure 1, if gas is included in the upper portion of the circulation pump 7, the cavitation phenomenon may be observed in the circulation pump and, in the worst case In this case, the bomb can be destroyed. In the opposite case, the phenomenon of gas inclusion will also occur in the upper portion of the shell 2, and the gas phase retention portion will be formed in the upper portion of the shell 2, whereby the upper portion of the reaction tubes, corresponding to to the gas retention portion will not be cooled by the heating medium Hm.

As measures to prevent gas retention, it is necessary to place a gas vent line to replace the gas in the gas layer with the heating medium Hm. For this purpose, the heating medium pressure of the heating medium supply line 8a should be increased, and the heating medium exhaust line 8b will be provided in an upper portion as far as possible to increase the pressure. in hull 2. Exhaust duct of heating means 8b should be provided at a higher position than upper tubular plate 5a. The flow direction of gaseous feedstock Rg in reaction tubes 1a, 1b and 1c can be upward or downward. However, a parallel flow is preferred over the flow of the heating medium.

The heating values in reaction tubes 1a, 1b and 1c are higher in the inlet holes and the hot spot formation position is often found at a position on the reaction tube tube axis, within a range of 300 to 1,000 m. from the entrance.

With respect to baffle plates, the hot spot position is often found in an area between the upper tubular plate 5a or the lower tubular plate 5b and the baffle plate 6a. By supplying the heating medium Hm having a controlled temperature directly to the positions of the reaction tube axes 1a, 1b and 1c, corresponding to the maximum temperature of the reaction tubes, the formation of the hot spot can be easily controlled. Accordingly, it is preferred that the macroscopic flow direction of the heating medium Hm and the flow direction of the gaseous feedstock Rg are identical, that is, to flow in parallel. The amount of heat transfer, that is, the amount of reaction heat, can be calculated by the heat transfer coefficient x heat transfer area x (catalyst layer temperature-heating medium temperature). Consequently, a method for lowering the amount of reaction heat per surface area (the thermal transfer area) of the reaction tube is effective for lowering the maximum temperature of the reaction tube.

To equalize the heating value of the reaction heat, at least two types of catalyst layers having different activities are filled in the same reaction tube. It is preferred that a catalyst layer having lower activity is filled at the inlet side, and a plurality of catalyst layers are filled at the reaction tube, so that the catalyst layer is changed one after another, having a larger flow activity after the peak temperature distribution.

As a method for controlling catalyst layer activity, a method of using a catalyst having a different activity by controlling catalyst composition or a method of controlling activity by mixing catalyst particles with inert particles to dilute the catalyst may be, for example, mentioned.

A catalyst layer having a high proportion of inert particles (the ratio of catalyst particles to mixed particles: dilution rate) is stuffed into the inert parts of reaction tubes 1a, 1b and 1c, and a catalyst layer having a ratio of low or zero dilution is filled in the back flow of the reaction tube. The dilution rate differs depending on the catalyst. However, the dilution rate at the previous stage is 0.3 to 0.7 in many cases. The later stage dilution rate of 0.5 to 1.0 is preferably used. Like the variation activity or catalyst dilution, two or three stages are usually applied. The dilution rate of the stuffed catalyst in reaction tubes 1a, 1b and 1c need not be equal for all tubes. For example, the maximum temperature of reaction tube 1a is high, whereby the possibility of catalyst deterioration is high. To avoid this deterioration, it is possible to decrease the dilution rate in the previous stage and, on the contrary, to increase the dilution rate in the later stage.

If the conversions in the reactions of the respective reaction tubes are different, the conversion or average yield across the reactor will be affected thereby. Therefore, it is preferred that the respective reaction tubes are adjusted to obtain the same conversion even if the dilution rate is changed. The present invention is suitably applied to a multitubular reactor for oxidation of propylene or isobutylene by the molecular oxygen containing gas, or a multitubular reactor for oxidation of (meth) acrolein by the molecular oxygen containing gas to obtain (meth) acrylic acid. As a catalyst to be used for propylene oxidation, a multicomponent composite metal oxide comprised basically of the Mo-Bi type is preferably used, and as a catalyst for producing acrolein oxidation acrylic acid, a composite oxide comprised basically of the type Mo-V is preferably used.

Propylene or isobutylene is oxidized in two steps, whereby two multitubular reactors can be used, and different catalysts can be filled in the respective reactors. As shown in Figure 5, the present invention may be applied in a case where the hull side of a reactor is divided into at least two compartments by an intermediate tubular plate, and then different catalysts may be filled thereon respectively to obtain (meth) acrylic acid in a reactor. EXAMPLES EXAMPLE 1 For conducting the propylene oxidation reaction, such as catalyst (A), a catalyst having a composition (atomic ratio) of Mo = 12, Bi = 5, Ni = 3, Co = 2, Fe = 0.4 , Na = 0.2, B = 0.4, K = 0.1, Si = 24 and O = x, (the oxide composition x is a value determined by the oxidation states of the respective metals; the same applies to below), and furthermore, as catalyst (B), a catalyst having a composition (atomic ratio) of Mo = 35, V = 7, Sb = 100, Ni = 43, Nb = 3, Cu = 9, Si = 20 and O = x, were produced, respectively, according to the usual methods for obtaining powder catalysts. The powder catalysts were molded, respectively, to form ring-shaped catalysts having an outside diameter of 5 mm, an inside diameter of 2 mm and a height of 4 mm, and used. A multitubular reactor with an inner shell diameter of 3,500 mm, having 9,000 stainless steel reaction tubes, as shown in Figure 1, was used, where the reaction tubes were 3,500 mm long, an internal diameter of 24 mm and an outside diameter of 28 mm respectively. The reaction tubes were not arranged in the round shape portion, with the central portion diameter equal to 500 mm in the shell.

The baffle plates were provided at equal intervals in the order of circular baffle plates 6a - 6b - 6a, and the respective baffle plate opening ratios were 18%. In addition, the baffle plates 6b had opening portion diameters of 1,480 mm, and the baffle plate 6b had an internal diameter of 3,170 mm.

In addition, as shown in the hull in Figure 1, the number of reaction tubes 1a was 1.534, that of reaction tubes 1c was 1.740 and the rest were reaction tubes 1b.

As the heating medium Hm, a Niter melt salt being a nitrate mixture was used, and was provided from the underside of hull 2.

As the reaction temperature, the temperature of Niter to be supplied to hull 2, measured by thermometer 14, was used. In addition, the Niter flow rate was controlled so that the temperature difference between the hull 2 inlet and outlet was 4 ° C.

In the respective reaction tubes, 1.5 l of catalyst (A) was filled, gaseous feedstock Rg with a propylene concentration of 9% by volume was supplied from a lower portion of the reactor at a nominal pressure of 74 kPa.

In reaction tubes 1a, 1b and 1c, thermometers 11 having 10 measuring points in the direction of each tube axis were inserted to measure temperature distribution. In each area of the reaction tubes 1a, 1b and 1c, two thermometers (six in total) are inserted.

In order to detect the maximum temperatures of the respective reaction tubes, precisely, the thermometer 11 measuring points were provided respectively at 250 mm intervals from the reaction tube inlet port to the 1,500 mm position and at 400 nm intervals at the beyond 1,500 mm. Maximum tube temperatures were recorded using these thermometers 11.

When the temperature of the heating medium Hm was set to 331 ° C, the average maximum temperature of the respective reaction tubes was 410 ° C in reaction tubes 1a, 390 ° C in reaction tubes 1b and 390 °. C in reaction tubes 1c. Furthermore, in this case, the conversion of propylene was found to be 97% and the yield 92%. EXAMPLE 2 Using the same reactor as in Example 1, gas containing molecular oxygen (oxygen concentration: 15% by volume) was supplied at a ratio of 35% by volume and reacted with the reactor outlet gas in Example 1 to produce acrylic acid.

In the respective reaction tubes, 1.2 l of catalyst (B) was filled. In addition, the reaction was conducted in the same manner as in Example 1, except that the temperature of the heating medium Hm was set at 275 ° C.

Average values of the maximum temperatures of the respective reaction tubes were 330 ° C in reaction tubes 1a, 300 ° C in reaction tubes 1b and 300 ° C in reaction tubes 1c. Furthermore, in this case, the conversion of propylene was found to be 99% and the yield was 90.5% by calculation based on propylene. EXAMPLE 3 The same reactor as that of Example 1 was used and the catalyst (A) and inert ring obtained by molding an inert material (alumina) were mixed 1: 1 and filled in the reaction tubes of their inlets to the position. 1,500 mm. In the remainder of the 1,800 reaction tubes, only catalyst (A) was filled and in the remaining 200 mm, inert aluminum bubbles were filled to the present reaction.

In addition, the reaction was conducted in the same manner as in Example 1, except that the temperature of the heating medium Hm was set at 335 ° C. As the thermometers to be used for measuring the catalyst layers in the reaction tubes, those having 15 measurement points were used, and the measurement was conducted at 200 mm intervals. The temperature distribution of the respective catalyst layers was measured, and the catalyst layers were found to have two maximum temperatures.

When presented as the primary maximum temperature and the secondary maximum temperature of the reaction tube inlets as for the respective mean values, in reaction tubes 1a, the primary maximum temperature i was 393 ° C and the maximum secondary temperature was 345 ° C. ° C, in reaction tubes 1b, the primary maximum temperature was 370 ° C and the secondary maximum temperature was 350 ° C and in reaction tubes 1c, the primary maximum temperature was 365 ° C and the maximum secondary temperature was of 380 ° C.

Compared to a case in which the catalyst was not diluted, the temperature of the heating medium Hm was 4 ° C higher. However, the respective maximum temperatures in the catalyst layers were lower by 10 to 20 ° C, even when higher temperatures were compared. Thus, the result shows that an extension in catalyst life and constant operation can be expected.

In addition, the total yield of acrolein and acrylic acid obtained from propylene was found to be 92.5%. COMPARATIVE EXAMPLE 1 The reaction was conducted in the same manner as in Example 2 except that the thermometers were not inserted into reaction tubes 1a and 1c, but the same thermometers as in Example 1 were inserted into reaction tubes 1b connected to all baffle plates and having a good thermal removal efficiency.

To achieve an conversion of 99% to 99.5% acrolein, the inlet temperature of the heating medium Hm was changed from 275 to 280 ° C, whereby the maximum value in the temperature distribution of the catalyst layers in the reaction 1b stood at 310 ° C.

By analysis of the gaseous reaction product, acrolein conversion was measured, whereby the conversion rate was found to be decreased to 97.9%. After that, the operation was continued, with which the conversion gradually decreased. Therefore, the inlet temperature of the heating medium Hm was further raised by 2 ° C to 282 ° C, whereby the conversion of acrolein was further decreased.

When the conversion of acrolein decreased to 95%, the reaction was suspended to check the catalyst in the reaction tubes. No abnormalities were observed in the catalyst in reaction tubes 1b and 1c. However, between reaction tubes 1a, in particular, the catalyst in approximately 350 reaction tubes 1a arranged in the vicinity of the reactor center has been found to visibly deteriorate and change in shape and lose its catalytic activity. The catalyst was presumably exposed to a high temperature of at least 400 ° C. INDUSTRIAL APPLICABILITY

In a process for catalytic vapor phase oxidation employing a multitubular reactor according to the present invention, the internal temperature of the reaction tubes having a catalyst filler disposed in the reactor shell is measured and based on that temperature. , the temperature and flow rate of a heating medium introduced into the hull are controlled, whereby in the production of (meth) acrylic acid or the like from propylene or isobutylene an uncontrolled reaction or early catalyst deterioration can be prevented. , and makes it possible to produce it consistently in high yield over a long period of time.

Claims (8)

1. Process for catalytic vapor phase oxidation, in which the gaseous feedstock is introduced for oxidation into the reaction tubes of a multitubular reactor, which is equipped with several catalyst-filled reaction tubes disposed within the reactor shell. in them and various baffle plates to vary the flow direction of a heating medium introduced into the shell, characterized in that the temperature of the catalyst filler in a reaction tube, which is not connected with at least one baffle plate, is measured. . 2. Process for catalytic vapor phase oxidation, in which the gaseous feedstock is introduced for oxidation into the reaction tubes of a multitubular reactor, which is equipped with several reaction tubes having catalyst filling arranged within the reactor shell. in them and various baffle plates to vary the flow direction of a heating medium introduced into the shell, characterized in that the temperature of the catalyst filler in a reaction tube, which is not connected to at least one baffle plate, and The temperature of the catalyst filling in a reaction tube, which is connected with all baffle plates, is measured. Process according to Claim 1 or 2, characterized in that the temperature or flow rate of the heating medium to be introduced into the shell is controlled based on the measured temperature of the catalyst. Process according to any one of claims 1 to 3, characterized in that the catalyst temperature is measured at 2 to 20 points in the direction of the reaction tube axis. Process according to any one of Claims 1 to 4, characterized in that the temperature of the catalyst is measured using a multipoint thermocouple. A process according to any one of claims 1 to 5, wherein the direction of the flow of gaseous raw material flowing in the reaction tubes and the direction of a macroscopic flow of the heating medium which flows in the hull they are identical. Process according to any one of claims 1 to 6, characterized in that several layers of catalyst having different activities are filled in the reaction tubes. Process according to any one of claims 1 to 7, characterized in that the gaseous feedstock contains propylene, isobutylene or (meth) acrolein as a material to be oxidized.